Gramophone pick-ups



May 16, 1961 R. w. BAYLIFF GRAMOPHONE PICK-UPS 2 SheetsSheet 1 iledSept. 22, 1958 Fig.1

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y 1961 R. w. BAYLIFF GRAMOPHONE PICK-UPS 2 Sheets-Sheet 2 Filed se p.22, 1958 United States Patent GRAMOPHONE PICK-UPS Raymond WilliamBaylilf, Wings, 15 Ormond Ave.,

Hampton, England Filed Sept. 22, 1958, Ser. No. 762,584

'Claimspriority, application Great Britain Oct. 8, 1957 Claims. (Cl.179100.41)

The present invention relates to gramophone pick-ups for use with soundrecords for stereophonic reproduction in which signals from two suitablyspaced microphones are recorded as modulations in the same sound groove,the two modulations producing vibrations of the pick-up stylus about twomutually perpendicular axes. In one system, using whatwill be called asymmetrically modulated sound groove, theseaxes are displaced by 45 oneither side of the vertical. In another system one axis is vertical,corresponding to hill and dale recording, and the other horizontal,corresponding to lateral recording.

With such a sound record it is required to be able to generate separatesignals from each modulation, such signals being amplified and" appliedto suitably spaced loudspeakers respectively.

A pick-up for such a purpose is required to operate in such a mannerthat interaction between the signal generating systems for the twomodulations is of a satisfactorily low order over the acoustic frequencyrange, and also that in neither set of signals shall the non-lineardistortion be significantly greater than is acceptable in a normalmonaural system.

The present invention has for its object to provide a pick-up wherebythese requirements can be met.

According to thepresent invention a gramophone pickup for stereophonicreproduction comprises a ferromagnetic armature adapted to carry astylus and mounted with freedom of movement in two modes, namely onecorresponding to lateral and the other to vertical movernents of thestylus, two separate magnetic cores each provided with a winding andeach having pole tips adjacent the armature, and one or more magnetsarranged to pass a polarising flux through the cores and armature, thearrangement being such that lateral movements of the stylus produce fluxchanges substantially only in one of the said windings and verticalmovements of the stylus produce flux changes substantially only in theother of the said windings.

In a preferred form of the invention the armature is elongated, and ismounted for rocking movement about an axis perpendicular to itslongitudinal axis between four pole tips. of one core, the rockingmovement producing flux changes in a coil surrounding the armature andconstituting one of the said windings, and the other core having twopole tips disposed above the armature in such a position that movementsof the armature in the direction of its longitudinal axis produce fluxchanges in one or more coils surrounding the said other core andconstituting the other of the said windings.

The invention will be described, by way of example, with reference tothe accompanying drawing, in which:

Fig. 1 is a view in part sectional elevational of one embodiment of theinvention,

Fig. 2 is an underside plan view of the embodiment of Fig. 1,

Fig. 3 is a view in front elevation of a part of a modification of theembodiment of Figs. 1 and 2.

Fig. 4 is a view in side elevation of the part in Fig. 3,

Fig. 5 is an underside plan view of another part of the modification ofFigs. 3 and 4,

Fig. 6 is a circuit diagram showing one form of coil connections thatmay be used, and

Fig. 7 is a diagram showing the preferred way in which the connectionsof Fig. 6 are made.

The embodiment illustrated in Figs. 1 and 2 is a modification of thepick-up described in the specification of my application Serial No.583,074 which is adapted for reproducing from lateral modulation only.

Referring to the drawings, anarmature 10 is a mild steel tube 2.5 mm.long, 0.4 mm. outside diameter and 0.0375 mm. wall thickness. The upperend of this armature is rigidly attached to one end of a cantileversupporting plate 11 constituted by a mild steel strip 0.0375 mm. thickhaving its plane at right angles to the length ofthe armature. The otherend of the plate 11 is firmly clamped by means such asare shown in theearlier specification hereinbefore mentioned (but not shown in thepresent drawings) to the body 13 of the pick-up. The plate 11 isprovided with a longitudinal stiffening ridge 14 extending along thecentre line of the plate. This ridge has a smaller depth than in theearlier specification in order to increase suitably the verticalcompliance C The compliances C and masses M are herein referred to thetip of a sapphire stylus 16 mounted in the lower end of the armature.The subscripts x, y and 2: refer to the three mutually perpendiculardirections shown in the drawing.

A thin steel wire of, for example, No. 48 S.W.G; which is not shown inthe drawing, is fixed at one end to the armature 10 close to the stylus16 and has its other end fixed to the body 13 as described in theearlier specification, this Wire being placed under tension and beingstraight and perpendicular to the lateral plane of vibra tion of thearmature in the direction y.

A pancake-shaped coil 17 is mounted to surround the armature with itsaxis along the longitudinal axis of the armature. A suitable permanentmagnet 33 is provided, fixed rigidly to the pick-up body 13, and softiron pole pieces 18 of this magnet have pole tips 18' and 18" extendingabove and below the coil 17 towards the armature. The upper pole tips18' have their upper surfaces chamfered as shown. The arrangement issuch that when the armature is in its rest position the magnetic fluxbetween the pole pieces is in the y direction, no flux traversing thearmature longitudinally.

The pole pieces 18 with their pole tips constitute one of the two coresreferred to, lateral movements of the stylus 16 (in the y direction)varying the flux distribution in this core and correspondingly varyingthe flux flowing longitudinally through the armature 10 and hencethrough the coil 17.

The other core 28 is constituted by 1.25 mm. diameter Radiometal rod,shaped as shown, and having pole tips separated by an air gap 31 ofabout 1 mm. These pole tips have their lower extremities approximately1.0 mm. above the upper end of the armature 10 and the front end of thesupport plate 11. The core 28 is in two like parts each surrounded by acoil 29, these coils being connected in series. An air gap 30 isprovided in the upper part of the core 28 in order to increase theincremental permeability in the presence of a strong magnetic polarisingfield. The air gap 30 also contributes to rendering the system 28, 29,3'1 symmetrical about the three major axes, and so achieves a reasonableimmunity from the effects of external interfering magnetic fields. Forthe same purpose the two coils 29 have equal numbers of turns and likedimensions.

The coil 17 has one end connected to a contact 34 and its other endconnected to a contact 35 to which one end of the series-connected coils29 are connected, so that the contact 35 is a common contact. The otherend of the coils 2 9 is connected to a further contact 36. Thesecontacts 34, 35 and 36 serve as output terminals for the pick-up.

In operation, when the two modulations of the sound groove are verticaland lateral, the lateral modulation is reproduced in the same manner aswith the pick-up of the earlier specification, signals corresponding tothis modulation being generatedlbetween the contacts 34 and 35.

So far as the reproduction of the vertical modulation is concerned, itwill .be noted that the front end of the support plate 11 and the upperend of the armature 10* will become magnetised by induction from themagnetic field existing between the upper .pole tips 18. Thesemagnetised parts may, therefore, be considered to behave as a smallmagnet with its poles separated in the y direction. As this srnallmagnet is displaced in the z direction, that is in a direction parallelto the longitudinal axis of the armature 10, by the action of thevertical modulation of the sound groove, it causes a varying magneticflux to traverse the core members 28 and coils 29. The E.M.F.-s therebyinduced in the coils 29 appear between the contacts 35 and 36.

One advantage of the pick-up described is that the provision of thefacility for reproduction of the vertical modulation does not involvethe provision of any extra vibratory parts beyond what are required forreproducing the lateral modulation, and additional mass loading is thusavoided.

In order to achieve a high degree of separation between the signalsgenerated in the two systems 10, 17, 18.and 10, 28, 29, provision ispreferably made for two mechanical adjustments although this is notessential. One of these, shown in Figs. 3 and 4, may be incorporated inthe mounting arrangements for the core members 28 to permit thesemembers to be moved laterally (i.e. in the direction y) by a smallamount and firmly clamped in a position in which a negligible output isobtained from the coils 28 which the stylus 16 is driven by a soundgroove which is modulated only laterally. Thus the core members 28 arecemented to a mounting block 38, for instance of nonmagnetic plasticwhich is fixed to the body 13 by means of screws 39 which pass throughslots 40* in the block 38.

The other provision that may be made is shown in Fig. and permits asmall lateral adjustment (i.e. in the y direction) of the pole pieces18, by means of which a setting can be found in which a negligibleoutput is obtained from the coil 17 when the stylus 16 is driven by asound groove modulated only vertically. Thus each pole piece 18 has anextension 41 in which is formed a slot 42. The pole pieces are clampedto the body 13 by screws 43 passing through the slots 42.

Owing to the increased verticalcompliance of the arma ture mounting incomparison with that in the pick-up described in the earlierspecification, there is no need for the special mounting, described inthe earlier specification, for preventing damage to the supporting plate11 and wire if the pick-up should be dropped upon the surface of arecord. Instead, it is sufficient to provide as shown in Fig. 1 smallblocks 37 of hard rubber or plastic in order to protect the stylus fromexcessive vertical displacement.

Suitable values of compliance C and mass M (as hereinbeforedefined) inthe three directions x, y and z in the pick-up described are as follows:

C 2.0 1 0- cm./dyne.

When the pick-up is for use with records bearing symmetricalmodulations, as hereinbefore referred to, which although still at rightangles to one another, have their axes rotated through 45 from thevertical, a sum and difference netwonk may be connected between thecontacts 34, 35 and 36 of Fig. 1, and output terminals. If the voltageat 34 with respect to 35 be L' and if the voltage at 36 with respect to35 be V, the network is so constituted that between one pair of outputterminals there is produced a voltage L'+V and between the other pair ofoutput terminals there is produced a voltage L'V. Preferably, however,the coils 29are each wound in duplicate thus providing as shown in Figs.3 and 4 two coils 29a, 29b or 2%, 29b on each limb of the core 28. Thecoils may then be connected as shown in Fig. 6 in such a manner that ifV is the voltage developed across each pair of coils 29, and if L is thevoltage developed across the coil 17, the voltage between terminals 34and 35 is LV and that between the terminals 36 and 35 is L+V.

The preferred way of interconnecting the .coils 29 in order to achievesymmetry and reduce the effect on the pick-up of interfering externalmagnetic fields is shown in Fig. 7, the core members 28 being indicatedin phantom. The coils are all wound in the same sense.

It will be appreciated that with the arrangement of Fig. 7 a flux changeproduced by the vertical movement of the stylus traverses the two coremembers 28 in series from one pole tip, around the system to the otherpole tip. Interfering fields (for example hum from transformers) tend totravel through the two core members in parallel, that is in the samedirection. Thus the coils 29a and 29a are connected in series in such away that signal voltages add whereas hum voltages subtract. The sameapplies to coils 29b and 29b.

I claim:

1. A gramophone pick-up for stereophonic reproduction comprising anelongated ferromagnetic armature, a stylus at one end of said armature,means supporting said armature with freedom of movement in two modes,namely a mode corresponding to vertical movement of said stylus and amode corresponding to horizontal move: ment of the stylus, a firstwinding surrounding said armature, a first magnetic core having fourpole tips adjacent said armature, two on each side thereofia secondmagnetic core having two pole tips adjacent the end of said armatureremote from said stylus, magnet means passing polarising flux throughsaid cores and 'said armature, and a second winding surrounding saidsecond core.

2. A gramophone pick-up according to claim 1, where: in said armaturesupporting means comprise a cantilever supporting plate having its freeend fixed to the end of said armature remote from said stylus.

3. A gramophone pick-up according to claim 2, wherein said supportingplate is of magnetic material;

4. A gramophone pick-up according to claim'l, further comprising threeoutput terminals, two of said terminals being connected to the ends ofone of saidwindings and the other said terminal being connected throughthe other said winding to a tap on said one winding.

5. A gramophone pick-up according to claim 1, further comprising threeoutput terminals, two of said terminals being connected to the ends ofone of said windings and the other said terminal being connected throughthe other said winding to the centre point of said one winding.

References Cited in the file of this patent UNITED STATES PATENTS

